JPH10135099A - Exposure device and exposure method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exposure device for preventing the occurrence of the variation of line width on a wafer face owing to the difference of photoresist film thickness on the wafer face and to provide the exposure method of a semiconductor wafer. SOLUTION: The exposure device 10 has a conventional exposure device 12, a first calculation means 14 and a second calculation means 16. The first calculation means 14 calculates predicted line width in an arbitrarily selected position in a sample wafer, based on a relation that the difference between preset line width and formed line width in the wafer face. Namely, the line width deviation distributes, according to a normalized distribution curve with respect to the distance from the wafer center and on line width measurement values measured in measurement positions, which are arbitrarily set along one diameter direction of the sample wafer and the direction orthogonal to the diameter direction. The second calculation means 16 calculates a necessary exposure value at the selected position, so that preset line width can be obtained based on predicted line width in accordance with the correlation relation of line width and the exposure value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exposure apparatus,
More specifically, the present invention relates to an exposure apparatus capable of exposing a pattern so that a formed line width becomes uniform in a wafer surface.

[0002]

2. Description of the Related Art In manufacturing a semiconductor device, when patterning is performed by photolithography, a pattern line width formed by exposing a photoresist film is an extremely important factor that affects the operation characteristics of the semiconductor device. In particular, MO
Since the gate length of the S transistor is one of the important factors that determine the operation speed of the semiconductor device, the design of the semiconductor device is set in consideration of the relationship between the transistor capacity and the gate length. With the demand for high integration and high-speed operation of semiconductor devices, the gate length is miniaturized according to the miniaturization of the design rule, and the application ratio of the photolithography technology increases the variation ratio of the gate length. It is becoming more and more difficult to suppress variations. If the variance in the dimensional accuracy of the gate length is large, the speed of the semiconductor device cannot be increased, and the product yield will be reduced. It has become important. Therefore, conventionally, a variation in gate length has been reduced by providing an anti-reflection film, or a variation in gate length has been reduced by using a light proximity effect control technique.

[0003]

However, in the above-mentioned conventional method, there is a limit in suppressing the variation in the gate length, and therefore, the performance of the MOS transistor of the product, particularly, the operation speed and the power consumption are varied. It was difficult to improve the product yield. Variations in line width such as gate length can be roughly classified into three types, each of which is considered to be caused by the following causes. 1) Variations between wafers and wafer lots Variations of this type are presumed to be due to temporal changes in the optimal exposure conditions, in-plane variations in photoresist film thickness, and variations between lots. 2) Variation in wafer surface This type of variation is presumed to be due to variations in photoresist film thickness within the surface and variations in the amount of developer supplied, and furthermore to variations in the height of the photoresist film surface of the wafer. . 3) Intra-shot variation It is estimated that this is due to the brightness of light in the exposure field, lens distortion, and pattern distortion. Of these three types of line width variations, line width variations in the wafer surface due to variations in photoresist film thickness are one of the most prominent variations, and are difficult to overcome with conventional techniques. Things.

An object of the present invention is to provide an exposure apparatus, a method of exposing a semiconductor wafer, and a method of preventing the occurrence of line width variations in a wafer surface due to a difference in photoresist film thickness in the wafer surface. It is to provide.

[0005]

In the process of investigating the cause of line width variation, the present inventors have found that the thickness of the photoresist film on the wafer is not uniform in the wafer surface, In the conventional exposure method, each shot is exposed at the same exposure time irrespective of the shot position in the wafer surface, although the thickness is gradually increased toward the peripheral portion. Focusing on the fact that the line width of the chip becomes thicker than the central part, we studied how to change the exposure amount according to the thickness of the photoresist film.

Since the line width differs depending on the thickness of the photoresist film, the difference between the set line width and the formed line width in the wafer plane, that is, the line width deviation is normal to the distance from the wafer center. If the empirical rule of distribution according to the distribution curve holds, and if other conditions are the same, the exposure amount,
For example, the inventors have noticed that the exposure time and the line width have a certain correlation, and have repeated confirmation experiments to complete the present invention. In the present specification, the line width refers to the pattern width of the photoresist film remaining after exposure and development when wiring is formed using a positive photoresist film, and the exposure and development when forming a contact. The groove width that exposes the underlayer after the formation.

In order to achieve the above object, based on the above findings, an exposure apparatus according to the present invention provides an exposure apparatus for exposing a pattern on a photoresist film on a wafer, wherein the exposure apparatus has a set line width and a predetermined line width within a wafer surface. The difference from the line width, that is, the relationship that the line width deviation is distributed according to the normal distribution curve with respect to the distance from the center of the wafer, and the diameter of one sample wafer exposed and developed under predetermined exposure and development conditions. Calculating a predicted line width at an arbitrarily selected position of the sample wafer based on the line width measurement values of the pattern measured at a plurality of measurement positions set along the direction and the direction orthogonal to the diameter direction thereof;
Calculating the required exposure amount at the selected position so as to obtain the set line width at the selected position according to the correlation between the line width and the exposure amount based on the predicted line width calculated by the first calculating unit. And a second calculating means for performing the calculation.

In the present invention, it is not necessary to set the measurement positions so that the measurement positions for measuring the line width of the sample wafer are at equal intervals, and the intervals may be different as described later. Further, the correlation between the line width to be used and the exposure amount is a relationship previously obtained by an experiment or the like. As the first and second calculation means, a known arithmetic device, for example, a small computer can be used. The exposure amount is a physical amount that has a one-to-one relationship with the line width. For example, when the exposure apparatus is a reduction projection exposure apparatus, the required exposure amount is defined by the exposure time, and the electron beam by the direct writing method is used. In the case of an exposure device,
The required exposure is defined by the exposure time and / or the exposure energy.

When a photoresist film is applied, wafers belonging to the same lot usually have the same photoresist film thickness distribution. The present inventor has developed an exposure method using the above-described exposure apparatus based on this empirical rule. An exposure method according to the present invention uses the above-described exposure apparatus to expose a pattern on a photoresist film on a wafer, wherein one of a plurality of wafers belonging to the same lot coated with the photoresist film is exposed. A wafer is selected as a sample wafer, a pattern is exposed and developed on a photoresist film on the sample wafer under predetermined exposure conditions, and a process is performed along a diameter direction of one of the sample wafers and a direction orthogonal to the diameter direction. The step of measuring the pattern forming line width at a plurality of set measurement positions, and the difference between the set line width and the forming line width in the wafer plane,
That is, a step of calculating a predicted line width at an arbitrarily selected position on the sample wafer based on the line width measurement value, according to a relationship that the line width deviation is distributed according to a normal distribution curve with respect to the distance from the wafer center, Calculating the required exposure amount at the selected position to obtain the set line width at the selected position based on the predicted line width according to the correlation between the line width and the exposure amount; And
Exposing the pattern with the required exposure calculated at the same position as the sample wafer selection position.

The exposure method of the present invention is not limited in its application, but can be suitably applied particularly when patterning by photolithography to form a gate of a MOS transistor.

[0011]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Example embodiment of the exposure apparatus is an embodiment of an exposure apparatus according to the present invention,
This is an example in which the present invention is applied to a reduction projection exposure apparatus. FIG. 1 is a block diagram showing the configuration of the exposure apparatus of the present embodiment. The exposure apparatus 10 of this embodiment includes a reduced projection exposure apparatus 12 (hereinafter simply referred to as a stepper 12) having the same configuration as that of the related art, a first calculation unit 14, and a second calculation unit 16.

If the predicted line width deviation of the formed pattern and the set line width are known, the predicted line width of the pattern can be obtained. Therefore, the first calculating means 14 has an empirical rule that the difference between the set line width and the formed line width in the wafer plane, that is, the line width deviation is distributed according to a normal distribution curve with respect to the distance from the wafer center. And, predetermined exposure, the line width measurement value measured at a plurality of measurement positions set at substantially equal intervals along the diameter direction of one of the sample wafers exposed and developed under development conditions and a direction orthogonal to the diameter direction of one of the developed sample wafers , A predicted line width at an arbitrarily selected position of the sample wafer is calculated. FIG. 2 shows a distribution of line width measurement values obtained by measuring the line width of a pattern actually formed on a sample wafer at measurement positions P1 to P5 along a diameter parallel to the orientation flat. FIG. 3 shows a distribution of line width measurement values obtained by measuring the line width of a pattern actually formed on a sample wafer at measurement positions P1 'to P5' along a diameter orthogonal to the orientation flat. 2 and 3, reference numeral 18 denotes a sample wafer.

The exposure amount, for example, the exposure time and the line width have a certain correlation, and are represented, for example, by a graph as shown in FIG. The second calculating means 16 selects a selected position based on the predicted line width obtained by the first calculating means 14 according to the correlation between the line width and the exposure time as shown in FIG. To calculate the required exposure. For example, FIG.
In the position of the star mark, the predicted line width can be calculated to be 0.38 μm by the second calculating means 14, and the required exposure time becomes 380 msec from FIG. On the other hand, the line width of the central portion P3 in FIG. 3 is 0.35 μm, and the required exposure time is 400
It can be calculated as msec. Therefore, the line width is 0.3
Exposure time required for 5 μm is 400 msec +
(400 msec-380 msec) = 420 msec.

In this embodiment, the exposure apparatus main body is a stepper. However, an electron beam exposure apparatus using a direct writing method can be used instead of the stepper. In that case, instead of the exposure time,
Exposure time (scan speed) and / or exposure energy is used.

[0015] Using the example above exposure apparatus 10 of the exposure method, as an example case of forming a positive photoresist pattern to form a gate electrode pattern of the MOS transistor, the embodiment of the present exposure method explain. 1) First, one wafer is selected from a plurality of wafers belonging to the same lot on which a photoresist film has been applied to be a sample wafer, and a pattern is exposed and developed on the sample wafer under predetermined exposure and development conditions. . 2) Next, as shown in FIGS. 2 and 3, a plurality of measurement positions P1 to P5 and P1 'to P5 set at substantially equal intervals along one diameter direction of the sample wafer and a direction orthogonal to the diameter direction. ', The line width of the pattern is measured.

3) The difference between the set line width and the formed line width in the wafer plane, that is, the line width deviation is distributed according to the normal distribution curve with respect to the distance from the wafer center, based on the measured line width. A predicted line width deviation at an arbitrarily selected position of the sample wafer, for example, a star mark position is calculated, and a predicted line width is obtained from the set line width and the predicted line width deviation. 4) Next, according to the correlation between the line width and the exposure amount as shown in FIG. 4, the required exposure amount at the selected position, for example, the required exposure time, is obtained so as to obtain the set line width at the selected position based on the predicted line width. It is calculated as described above. Subsequently, for example, as shown in FIG. 5, the required exposure time is calculated for each selected position. In the case of the present embodiment, the positive photoresist film is formed relatively thinly and uniformly at the center of the wafer as compared with the periphery thereof. For example, when the line width is 0.32 μm,
The optimal exposure time is 400 msec. On the other hand, in the peripheral portion of the wafer, since the thickness of the photoresist film is relatively large, an exposure time of 420 msec to 450 msec is required to make the line width the same at 0.32 μm, depending on the exposure position. In FIG. 5, reference numeral 20 denotes a wafer to be patterned, and reference numeral 22 denotes each chip on the wafer 20. In FIG. 5, the numerical value shown at each selected position is the exposure time, which is a unit of msec.
Is omitted. 5) Subsequently, the pattern is exposed on the wafer other than the sample wafer at the same position as the sample wafer selection position with the calculated required exposure amount.

In the above-described embodiment, the measurement positions P1 to P5 are set at equal intervals, but need not necessarily be set at equal intervals. For example, P1 and P5 are provided around the wafer, P3 is provided at an arbitrary position between P1 and P5, and P2 is provided.
May be provided at any position between P1 and P3, and P4 may be provided at any position between P3 and P5. Further, the thickness distribution of the photoresist film slightly depends on the surface pattern of the device chip formed on the wafer, but rather depends on the type and rotation speed of the spin coater for applying the photoresist liquid. . Therefore, the spin coater used in the process is operated at the set number of revolutions to apply a photoresist liquid on the sample wafer, and data on the line width distribution is obtained in advance as shown in the lower graph of FIG. Then, for the same wafer as the sample wafer, the line width is measured at any one of the measurement positions P1, P2, and P3 in the actual process, and a graph passing the measurement value with the same waveform as the lower graph is shown. By drawing like the upper graph shown in FIG. 6, the line width distribution of all the wafer regions can be estimated.

[0018]

According to the structure of the present invention, the line width deviation is distributed according to the normal distribution curve with respect to the distance from the wafer center, based on the line width measurement value of the exposed and developed sample wafer. Calculate the predicted line width at an arbitrarily selected position on the sample wafer, and obtain the required line width at the selected position based on the predicted line width according to the correlation between the line width and the exposure amount. The amount is calculated, and the pattern is exposed at a selected position on the wafer with the exposure amount. By applying the present invention, a pattern with a uniform line width can be formed on a wafer in the plane of the wafer, so that a high-density semiconductor device operating at a high speed can be manufactured with a high product yield.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an embodiment of an exposure apparatus according to the present invention.

FIG. 2 is a graph showing line width measurements at measurement locations along the diameter in a direction parallel to the orientation flat.

FIG. 3 is a graph showing line width measurements at measurement locations along a diameter in a direction perpendicular to the orientation flat.

FIG. 4 is a graph showing a relationship between an exposure time and a line width.

FIG. 5 is a diagram showing a distribution of exposure time of each chip on a wafer.

FIG. 6 is a graph showing a line width distribution.

[Explanation of symbols]

10 an embodiment of the exposure apparatus according to the present invention, 12 stepper, 14 first calculating means, 16 second calculating means,
18 wafer, 20 chip to be patterned, 2
2 ... Tip.

Claims (4)

[Claims] In an exposure apparatus for exposing a pattern on a photoresist film on a wafer, a difference between a set line width and a formed line width in a wafer surface, that is, a line width deviation is normalized with respect to a distance from the wafer center. The relationship of being distributed according to the distribution curve, and measurement at a plurality of measurement positions set along one diameter direction of the sample wafer exposed and developed under predetermined exposure and development conditions and a direction orthogonal to the diameter direction. First calculating means for calculating a predicted line width at an arbitrarily selected position on the sample wafer based on the measured line width of the pattern, and a line width based on the predicted line width calculated by the first calculating means. And a second calculating means for calculating a required exposure amount at the selected position so as to obtain a set line width at the selected position in accordance with a correlation between the exposure value and the exposure amount. 2. When the exposure apparatus is a reduction projection exposure apparatus, the required exposure amount is defined by an exposure time. When the exposure apparatus is an electron beam exposure apparatus using a direct writing method, the required exposure amount is determined by an exposure time and / or an exposure time. 2. The exposure apparatus according to claim 1, wherein the exposure apparatus is defined by exposure energy. 3. An exposure method for exposing a pattern on a photoresist film on a wafer, wherein one wafer is selected from a plurality of wafers belonging to the same lot coated with the photoresist film and used as a sample wafer.
Exposing and developing a pattern on a photoresist film on a sample wafer under predetermined exposure conditions; and developing a pattern at a plurality of measurement positions set along one diameter direction of the sample wafer and a direction orthogonal to the diameter direction. The step of measuring the formed line width, and the difference between the set line width and the formed line width in the wafer plane, that is, the line width according to the relationship that the line width deviation is distributed according to the normal distribution curve with respect to the distance from the wafer center. Based on the measurements,
Calculating a predicted line width at an arbitrarily selected position on the sample wafer; and then obtaining a set line width at the selected position based on the predicted line width according to the correlation between the line width and the exposure. Calculating the required exposure amount, and exposing the pattern with the calculated required exposure amount on the photoresist film of the wafer other than the sample wafer and at the same position as the sample wafer selection position. Characteristic exposure method. 4. A wafer in which a photoresist film is formed on a polysilicon layer formed as a gate layer, and is patterned by photolithography.
The exposure method according to claim 3, wherein the method is applied when forming a gate of an S transistor.